From mboxrd@z Thu Jan 1 00:00:00 1970 Message-Id: <20080328015238.519230000@nick.local0.net> Date: Fri, 28 Mar 2008 12:52:38 +1100 From: npiggin@suse.de Subject: [patch 0/7] 2.6.25-rc5-mm1: VM_MIXEDMAP, pte_special, xip series Sender: owner-linux-mm@kvack.org Return-Path: To: akpm@linux-foundation.org Cc: Linus Torvalds , Jared Hulbert , Carsten Otte , Martin Schwidefsky , Heiko Carstens , linux-mm@kvack.org List-ID: -- Hi, This series introduces some important infrastructure work that I hope can go in the next merge window. It has been quite widely reviewed and has had a bit of testing (I have just tested XIP on brd on 2.6.25-rc5-mm1). The overall result is that: 1. We now support XIP backed filesystems using memory that have no struct page allocated to them. And patches 6 and 7 actually implement this for s390. This is pretty important in a number of cases. As far as I understand, in the case of virtualisation (eg. s390), each guest may mount a readonly copy of the same filesystem (eg. the distro). Currently, guests need to allocate struct pages for this image. So if you have 100 guests, you already need to allocate more memory for the struct pages than the size of the image. I think. (Carsten?) For other (eg. embedded) systems, you may have a very large non- volatile filesystem. If you have to have struct pages for this, then your RAM consumption will go up proportionally to fs size. Even though it is just a small proportion, the RAM can be much more costly eg in terms of power, so every KB less that Linux uses makes it more attractive to a lot of these guys. 2. VM_MIXEDMAP allows us to support mappings where you actually do want to refcount _some_ pages in the mapping, but not others, and support COW on arbitrary (non-linear) mappings. Jared needs this for his NVRAM filesystem in progress. Future iterations of this filesystem will most likely want to migrate pages between pagecache and XIP backing, which is where the requirement for mixed (some refcounted, some not) comes from. 3. pte_special also has a peripheral usage that I need for my lockless get_user_pages patch. That was shown to speed up "oltp" on db2 by 10% on a 2 socket system, which is kind of significant because they scrounge for months to try to find 0.1% improvement on these workloads. I'm hoping we might finally be faster than AIX on pSeries with this :). My reference to lockless get_user_pages is not meant to justify this patchset (which doesn't include lockless gup), but just to show that pte_special is not some s390 specific thing that should be hidden in arch code or xip code: I definitely want to use it on at least x86 and powerpc as well. There are basically no clashes between mainline and -mm, btw. Thanks, Nick -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org